Conventional dampers, or shock absorbers, used in automotive and other vehicular suspension systems, provide passive vibration control with a constant damping coefficient. To achieve a passive damping force that accentuates the comfort of the vehicle's ride as opposed to its handling dynamics, a low damping force or “soft” setting is used. By contrast, to achieve a high damping force that accentuates the handling dynamics of the vehicle as opposed to its ride comfort, a high damping force or “hard” setting is used. The conventional design of dampers used to achieve these various handling characteristics generally include an outer cylinder or shock body that coaxially houses a slidable piston head and piston rod immersed in a damping fluid. In accordance with these embodiments, the piston rod exits through one end of the shock body, yet is closed and sealed at this location so that the inner shock body volume is divided into two fluid filled chambers. These fluid chambers are communicative through valving integrated into the piston structure, and as such, a shock absorber configured for “hard” damping has valving which provides a restricted flow path for fluid to communicate between chambers, while a shock absorber configured for “soft” damping has valving which provides a less restricted fluid flow path between chambers. The end of the piston rod extending outward from the shock body is equipped with a mounting apparatus for attachment to either the sprung or unsprung vehicle mass. Likewise, the end of the shock body opposite the exit of the piston rod is equipped with a mounting apparatus for attachment to the vehicle mass, sprung or unsprung, which is not attached to the piston rod.
Semi-active damping systems are used to mitigate the tradeoff characteristics associated with passive dampers. A semi-active damper can vary its damping force across a force range in order to provide “hard” and “soft” damping responses dependent on a variety of driving scenarios. In typical vehicle operating conditions, imperfections in the driving surface induce small displacement, high frequency vibrations that are best damped with a “soft” damping coefficient capable of minimizing the transmission of vibration to the vehicle operator. However, during rapid driving maneuvers, as such would be experienced in panic or racing scenarios, it is desirable to have a “hard” damping coefficient which will minimize the roll and pitch of the vehicle body, consequently improving vehicle control. The performance quality of a semi-active damper is largely dependent on the magnitude of its damping force range and the rate at which it can transition between different damping forces.
A number of semi-active damping methods have been developed to maximize the two aforementioned performance measures. Several previous systems have employed the use of a rotary valve, capable of restricting or unrestricting flow paths between the fluid chambers. Other systems have employed the use of multiple pistons disposed within the shock body, those pistons being equipped with valve assemblies capable of biasing load magnitudes between one another and being dependent on compression or rebound travel and other input driving conditions. These valve assemblies are often driven with stepper motors. Other systems choose to increase or decrease fluid restriction at the orifice of the piston flow path. Semi-active damping by this method is often accomplished with an actuated disk valve or other orifice adjuster that controls the geometry of the cross-sectional orifice profile. In accordance with other systems, the walls of the outer cylinder are adjustably deformed to alter the volume and pressure of the working fluid chambers that directly influence damping characteristics. Still other methods of semi-active damping teach away from fluid flow path variation and choose to directly vary the fluid properties instead. Such semi-active damping methods often employ a magnetorheological oil as the working fluid and an electromagnet housed within the piston which is capable of altering the fluid properties of the oil, particularly shear stress, in response to the magnitude of the generated magnetic field.
Deformable membranes, rubbers, and elastomers have also been used as key structures to certain semi-active damping methods. One such method employs a passive rubber elastic body to readily absorb high frequency, low displacement vibration while a separate oscillation plate is actively actuated to best handle large displacement vibration and to vary the overall damping coefficient of the semi-active damping apparatus. Yet another method teaches semi-active damping through the use of a gas-filled, flexible membrane sandwiched between two axially spaced pistons on the same piston rod. As the piston rod moves during rebound or compression strokes, compressed gas pumped into the flexible membrane engages the fluid in a pressure-transmitting manner by means of the membrane wall. Thus, a highly pressurized flexible membrane will absorb minimal pressure from the working fluid and will only deform in small amounts, resulting in a high internal pressure within the shock body and a correspondingly high damping force. In the alternative, some systems teach that the flexible membrane may be less pressurized, so as to deform during fluid interaction, reducing the overall internal pressure, and producing a low damping force. In either case, both systems teach that at no point should the flexible membrane be exposed to frictional contact with the inner cylinder walls.
The present invention is intended to improve upon and resolve some of the known deficiencies associated with the various conventional systems discussed above.